package sym.qrcode.decoder;

final class FormatInformation {

	private static final int FORMAT_INFO_MASK_QR = 0x5412;

	/**
	 * See ISO 18004:2006, Annex C, Table C.1
	 */
	private static final int[][] FORMAT_INFO_DECODE_LOOKUP = {
			{ 0x5412, 0x00 }, { 0x5125, 0x01 }, { 0x5E7C, 0x02 },
			{ 0x5B4B, 0x03 }, { 0x45F9, 0x04 }, { 0x40CE, 0x05 },
			{ 0x4F97, 0x06 }, { 0x4AA0, 0x07 }, { 0x77C4, 0x08 },
			{ 0x72F3, 0x09 }, { 0x7DAA, 0x0A }, { 0x789D, 0x0B },
			{ 0x662F, 0x0C }, { 0x6318, 0x0D }, { 0x6C41, 0x0E },
			{ 0x6976, 0x0F }, { 0x1689, 0x10 }, { 0x13BE, 0x11 },
			{ 0x1CE7, 0x12 }, { 0x19D0, 0x13 }, { 0x0762, 0x14 },
			{ 0x0255, 0x15 }, { 0x0D0C, 0x16 }, { 0x083B, 0x17 },
			{ 0x355F, 0x18 }, { 0x3068, 0x19 }, { 0x3F31, 0x1A },
			{ 0x3A06, 0x1B }, { 0x24B4, 0x1C }, { 0x2183, 0x1D },
			{ 0x2EDA, 0x1E }, { 0x2BED, 0x1F }, };

	/**
	 * Offset i holds the number of 1 bits in the binary representation of i
	 */
	private static final int[] BITS_SET_IN_HALF_BYTE = { 0, 1, 1, 2, 1, 2, 2,
			3, 1, 2, 2, 3, 2, 3, 3, 4 };

	private final ErrorCorrectionLevel errorCorrectionLevel;
	private final byte dataMask;

	private FormatInformation(int formatInfo) {
		// Bits 3,4
		errorCorrectionLevel = ErrorCorrectionLevel
				.forBits((formatInfo >> 3) & 0x03);
		// Bottom 3 bits
		dataMask = (byte) (formatInfo & 0x07);
	}

	static int numBitsDiffering(int a, int b) {
		a ^= b; // a now has a 1 bit exactly where its bit differs with b's
		// Count bits set quickly with a series of lookups:
		return BITS_SET_IN_HALF_BYTE[a & 0x0F]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 4 & 0x0F)]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 8 & 0x0F)]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 12 & 0x0F)]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 16 & 0x0F)]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 20 & 0x0F)]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 24 & 0x0F)]
				+ BITS_SET_IN_HALF_BYTE[(a >>> 28 & 0x0F)];
	}

	/**
	 * @param maskedFormatInfo1
	 *            format info indicator, with mask still applied
	 * @param maskedFormatInfo2
	 *            second copy of same info; both are checked at the same time to
	 *            establish best match
	 * @return information about the format it specifies, or <code>null</code>
	 *         if doesn't seem to match any known pattern
	 */
	static FormatInformation decodeFormatInformation(int maskedFormatInfo1,
			int maskedFormatInfo2) {
		FormatInformation formatInfo = doDecodeFormatInformation(
				maskedFormatInfo1, maskedFormatInfo2);
		if (formatInfo != null) {
			return formatInfo;
		}
		// Should return null, but, some QR codes apparently
		// do not mask this info. Try again by actually masking the pattern
		// first
		return doDecodeFormatInformation(maskedFormatInfo1
				^ FORMAT_INFO_MASK_QR, maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR);
	}

	private static FormatInformation doDecodeFormatInformation(
			int maskedFormatInfo1, int maskedFormatInfo2) {
		// Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
		int bestDifference = Integer.MAX_VALUE;
		int bestFormatInfo = 0;
		for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.length; i++) {
			int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
			int targetInfo = decodeInfo[0];
			if (targetInfo == maskedFormatInfo1
					|| targetInfo == maskedFormatInfo2) {
				// Found an exact match
				return new FormatInformation(decodeInfo[1]);
			}
			int bitsDifference = numBitsDiffering(maskedFormatInfo1, targetInfo);
			if (bitsDifference < bestDifference) {
				bestFormatInfo = decodeInfo[1];
				bestDifference = bitsDifference;
			}
			if (maskedFormatInfo1 != maskedFormatInfo2) {
				// also try the other option
				bitsDifference = numBitsDiffering(maskedFormatInfo2, targetInfo);
				if (bitsDifference < bestDifference) {
					bestFormatInfo = decodeInfo[1];
					bestDifference = bitsDifference;
				}
			}
		}
		// Hamming distance of the 32 masked codes is 7, by construction, so <=
		// 3 bits
		// differing means we found a match
		if (bestDifference <= 3) {
			return new FormatInformation(bestFormatInfo);
		}
		return null;
	}

	ErrorCorrectionLevel getErrorCorrectionLevel() {
		return errorCorrectionLevel;
	}

	byte getDataMask() {
		return dataMask;
	}

	public int hashCode() {
		return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
	}

	public boolean equals(Object o) {
		if (!(o instanceof FormatInformation)) {
			return false;
		}
		FormatInformation other = (FormatInformation) o;
		return this.errorCorrectionLevel == other.errorCorrectionLevel
				&& this.dataMask == other.dataMask;
	}

}
